I think I would be generous if I stated 10% of the .net applications ran on Mono instead of MS CLR without source modifications. I even doubt more then 60% of the .net applications ran on .net Core (needed for other platforms then Windows) without modifications.
Meaning .net has nowhere near the "write once, run anywhere" support Java has.
Meaning .net has nowhere near the "write once, run anywhere" support Java has.